This application is based on Japanese Patent Applications Nos. 2000-160245 and 2000-368341, filed on May 30, 2000 and Dec. 4, 2000, respectively, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a taking lens device. More specifically, the present invention relates to a taking lens device that optically takes in an image of a subject through an optical system and then outputs the image as an electrical signal by means of an image sensor, for ex ample, a taking lens device that is used as a main component of a digital still camera, a digital video camera, or a camera that is incorporated in or externally fitted to a device such as a digital video unit, a personal computer, a mobile computer, a portable telephone, or a personal digital assistant (PDA). The present invention relates particularly to a taking lens device which is provided with a compact, high-zoom-ratio zoom lens system.
2. Description of Prior Art
In recent years, with the explosive spread of portable telephones and portable information terminals called PDAs an increasing number of models have been incorporating a compact digital camera, or digital video unit employing a CCD (charge-coupled device) or CMOS (complementary metal-oxide semiconductor) sensor as an image sensor. When such a digital camera, or the like, is miniaturized using an image sensor with a relatively small effective image-sensing surface area, its optical system also needs to be miniaturized accordingly. As compact zoom lenses with a small number of lens elements for use in a digital camera, or like, provided with an image sensor with a small effective area, Japanese Patent Application Laid-Open No. H11-72702, Japanese Patent Application Laid Open Open No. H1-191820, U.S. Pat. No. 5,745, 301, and others, propose a three-unit zoom lenses of a negative-positive-positive type composed of, from the object t side, a first lens unit having a negative optical power, a second lens unit having a positive optical power, and a third lens unit having a positive optical power. This type of lens includes a minimum number of movable lens units and has a simple mechanical structure, and is thus suitable as a low-cost zoom lens.
In the zoom lens proposed in Japanese Patent Application Laid-Open No. H11-72702 mentioned above, the individual lens units are each composed of one lens element, and thus, the entire zoom lens is composed of three lens elements in total. However, this arrangement includes a diffractive optical element, and therefore the zoom lens, when used as a taking lens system, suffers from ghosts caused by second- and third-order light. This makes the zoom lens somewhat unsatisfactory in image-sensing performance. Moreover, the aerial distance between the second and the third lens units is considerably long at the wide-angle end. This makes the optical total length of the zoom lens unduly long.
In the zoom lens proposed in Japanese Patent Application Laid-Open No. H1-191820 mentioned above, the first lens unit is composed of one lens element, the second lens unit is composed of one lens element, and the third lens unit is composed of two lens elements; thus, the entire zoom lens is composed of four lens elements in total. In this zoom lens, the third lens unit is given a relatively strong optical power, and therefore requires two lens elements. This makes it difficult to reduce the cost and size of the zoom lens. Moreover, this zoom lens offers a zoom ratio as low as about 2xc3x97 and a dark f-number. In the zoom lens proposed in U.S. Pat. No. 5,745,301, mentioned above, the first lens unit is kept stationary during zooming. As a result, the zoom lens offers a zoom ratio as low as about 2xc3x97, at most.
An object of the present invention is to provide an optical, or a taking lens device that allows both cost reduction and miniaturization and that is provided with a high-zoom-ratio zoom lens system that offers a bright f-number and a zoom ratio as high as about 3xc3x97.
To achieve the above object, according to one aspect of the present invention, an optical, or a taking lens device is provided with: a zoom lens system that is comprised of a plurality of lens units and that achieves zooming by varying the unit-to-unit distances; and an image sensor that converts an optical image formed by the zoom lens system into an electrical signal. The zoom lens system comprises, from the object side thereof to an image side thereof, a first lens unit having a negative optical power, a second lens unit having a positive optical power, and a third lens unit having a positive optical power. Here, the first, the second, and the third lens units are each comprised of one lens element, and at least the first and second lens units are moved along the optical axis during zooming. Moreover the following conditional formula is fulfilled:
0.2 less than tW2-3/fW less than 1.2
where
tW2-3 represents the optical path length from the most image-side lens surface in the second lens unit to the most object-side lens surface in the third lens unit at the wide-angle end; and
fW represents the focal length of the entire zoom lens systems at the wide-angle end.
According to another aspect of the present invention, an optical, or a taking lens device is provided with a zoom lens system that is comprised of a plurality of lens units and that achieves zooming by varying the unit-to-unit distances; and an image sensor that converts an optical image formed by the zoom lens system into an electrical signal. The zoom lens system is comprised of, from the object side thereof to the image side thereof, a first lens unit having a negative optical power, a second lens unit having a positive optical power, and a third lens unit having a positive optical power. Here, at least the first and second lens units are moved along the optical axis during zooming. Moreover, the following conditional formula is fulfilled:
7 less than f3/fW less than 20
where
f3 represents the focal length of the third lens unit; and
fW represents the focal length of the entire zoom lens system at the wide-angle end.
According to another aspect of the present invention, an optical, or a taking lens device is provided with: a zoom lens system that is comprised of a plurality of lens units and that achieves zooming by varying the unit-to-unit distances; and an image sensor that converts an optical image formed by the zoom lens system into an electrical signal. The zoom lens system comprises, from the object side thereof to the image side thereof, a first lens unit having a negative optical power, a second lens unit having a positive optical power, and a third lens unit having a positive optical power. Here, the first lens unit is comprised of one negative lens element having a sharp curvature toward the image side. Moreover, the following conditional formula is fulfilled:
0.2 less than t1/Yxe2x80x2 less than 1.2
where
t1 represents the axial thickness of the first lens unit from the most object-side lens surface thereof to the most image-side lens surface thereof; and
Yxe2x80x2 the maximum image height.